One proposed internal combustion engine system, having an engine and an EGR device that performs an exhaust gas recirculation (EGR) where exhaust from the engine is supplied to an intake system of the engine, sets one curve as an execution operation curve among several operation curves defining a relation between a rotation speed and a torque of the engine, and controls the engine based on the set execution operation curve and a power demand required for the engine (see, for example, Patent Document 1). In this internal combustion engine system, the engine is controlled based on the power demand required for the engine with the execution operation curve set to be, for example, a fuel economy prioritized operation curve for operating the engine without performing the EGR, and a high EGR operation curve and a low EGR operation curve for outputting a smaller torque from the engine with the EGR performed than the torque in the fuel economy prioritized operation curve.    Patent Document 1: Japanese Patent Laid-Open No. 2004-360672